Increased initial cement–bone interlock correlates with reduced total knee arthroplasty micro-motion following in vivo service
Introduction
Over 600,000 total knee arthroplasties (TKAs) are performed in the US each year and the probability of needing a revision during the lifetime of the patient has been estimated to be 15% for males and 17.5% for females (Losina et al., 2012). Loosening of the tibial component is the most common cause of knee arthroplasty failure, but details about how loosening occurs is not fully understood. Aseptic loosening of cemented implants is often seen as a progression of radiolucent lines on x-ray at the interface between the cement and bone (Schneider and Soudry, 1986). At this point, gaps can form between the cement and bone and are often filled with fibrocartilage tissue (Hori and Lewis, 1982). Poor penetration of cement into the bone bed at the time of surgery increases the propensity for radiolucency formation (Ritter et al., 1994).
Pressurization of cement into trabecular bone results in a mechanical interlock between the cement and bone and this provides the initial fixation for the implant. However, with in vivo service, the trabeculae that interlock with the cement layer can resorb. A recent morphological study of postmortem retrieved tibial trays showed that 75% of the cement–bone interlock was lost within 10 years of in vivo service (Miller et al., 2014). These findings suggest that the fixation that exists at the completion of surgery does not remain over the functional lifetime of the joint arthroplasty. Excessive trabecular bone resorption at the cement–bone interface could contribute to increased micro-motion and eventual implant loosening.
The goal of this study was to determine the influence of the initial state of cement–bone interlock on the loss of trabecular interlock and interface micro-motion following in vivo service. This was accomplished using en bloc postmortem-retrieved tibial components from TKAs; these implants were not revisions obtained for a loose implant. We hypothesized that tibial components with more initial interlock between cement and bone would maintain more interlock with in vivo service and have less micro-motion at the cement–bone interface.
Section snippets
Specimen preparation
Ten fresh-frozen cemented total knee arthroplasties (TKAs) were obtained en bloc from the Anatomical Gift Program at SUNY Upstate Medical University (Table 1). All components had metal tibial trays with stems/keels and polyethylene inserts. All tibial components were determined to be radiographically well fixed (radiolucent lines less than 2 mm in 1 or fewer zones).
Articulating surface wear was quantified using the grading scheme of Hood et al. (1983) for abrasion, burnishing, cement debris,
Results
The lateral specimen from Implant C failed during preparation due to a very weak cement–bone interface leaving 23 test specimens from 12 TKAs for testing and analysis. Specimens had a wide range of cement–bone interlock, from laboratory prepared specimens where there was no resorption of the trabecular bone (Fig. 4A), to postmortem retrievals with some remaining interlock (Fig. 4B), to specimens with little or no bone in the interdigitated region (Fig. 4C and D). The mean initial
Discussion
Postmortem retrieved tibial components from cemented total knee arthroplasties (TKA) were used to determine if implants that started with better initial interlock to bone maintained interlock with in vivo service, and also had greater mechanical stability. There was a loss of cement–bone interlock with in vivo service, and specimens with greater initial interlock maintained more interlock with time in service. With functional loads applied to the sagittal sections, there was less interface
Conflict of interest statement
Timothy Izant serves as a paid consultant for Stryker Orthopaedics for clinical total joint replacement studies unrelated to the content of this manuscript. All other authors have no conflicts of interest to disclose.
Acknowledgments
The research reported in this publication was supported by the National Institute of Arthritis and Musculoskeletal and Skin Diseases of the National Institutes of Health under Award number AR42017. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. The authors would like to acknowledge the assistance of Dan Jaeger for providing the postmortem retrievals and tissue from the SUNY Upstate Anatomical
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